This invention is directed to high molecular weight water-soluble polymers derived from zwitterionic monomer units, nonionic monomer units and at least one cationic or anionic monomer unit, and to the use of the polymers in papermaking processes.
In the manufacture of paper, an aqueous cellulosic suspension or slurry is formed into a paper sheet. The cellulosic slurry is generally diluted to a consistency (percent dry weight of solids in the slurry) of less than 1 percent, and often below 0.5 percent, ahead of the paper machine, while the finished sheet must have less than 6 weight percent water. Hence, the dewatering aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
The least costly dewatering method is drainage, and thereafter more expensive methods are used, including vacuum pressing, felt blanket blotting and pressing, evaporation and the like, and any combination of such methods. Because drainage is both the first dewatering method employed and the least expensive, improvements in the efficiency of drainage will decrease the amount of water required to be removed by other methods and improve the overall efficiency of dewatering, thereby reducing the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency and cost of manufacture is the retention of furnish components on and within the fiber mat being formed during papermaking. A papermaking furnish contains particles that range in size from about the 2 to 3 millimeter size of cellulosic fibers to fillers measuring only a few microns. Within this range are cellulosic fines, mineral fillers (employed to increase opacity, brightness and other paper characteristics) and other small particles that generally, without the inclusion of one or more retention aids, would pass through the spaces (pores) between the cellulosic fibers in the fiber mat being formed.
Typical retention aids include high molecular weight cationic or anionic synthetic polymer flocculants, composed of one or more nonionic monomers and one or more cationic or anionic monomers. The flocculant functions by binding the particles into large agglomerates. The presence of such large agglomerates in the furnish increases retention and drainage. The agglomerates are filtered out of the water onto the fiber web, where unagglomerated particles would otherwise generally pass. The presence of agglomerates allows water to pass more easily from the furnish through the pores surrounding them.
Other points in the papermaking process where material savings are important include pulp washers or thickeners. These processes filter the pulp with the purpose of displacing unwanted soluble or colloidal materials out of the pulp suspension, or thickening the pulp for a subsequent processing step. Valuable filler or cellulose fines can be lost during either thickening or washing processes. The addition of treatment additives, such as coagulants or flocculants, can be beneficial to the efficiency of these processes.
In many papermaking furnishes, particularly furnishes containing recycled fibers, there may be anionic substances that compete with the target anionic materials to be flocculated. When the target filler and fiber surfaces must compete for polymer with anionic solutes or colloids (anionic xe2x80x9ctrashxe2x80x9d), the flocculation efficiency is dramatically decreased because of the reduction in available cationic sites within the polymer. To circumvent this problem, one has traditionally complexed the detrimental anionic substances using a cationic coagulant. When the coagulant neutralizes the anionic charge on the high surface area of the detrimental anionic substances, the flocculant then remains xe2x80x9cfreexe2x80x9d to aggregate the remaining anionic fiber and filler surfaces, which is the desired result. However, fluctuations in charge demand of the process water owing to varying levels of the soluble detrimental anionic substances means that the coagulant dose will have to change in order to achieve the same extent of neutralization. Although eliminating the variations in flocculation performance is critical to maintaining process control and consistent operation, maintaining a constant solution charge prior to flocculant addition can be quite difficult in practice. An alternative approach to charge neutralization using coagulant addition is adding a flocculant that, by design, is resistant to changes in anionic trash levels and concentrations of charged species in solution.
One example of such a flocculant is poly(acrylamide), which is a neutral, uncharged homopolymer. Another example is uncharged polymers composed of one or more zwitterionic monomers and one or more nonionic monomers, disclosed in published International Application Number PCT/US00/17841.
We have discovered that high molecular weight, charged polymers made from one or more nonionic monomers, one or more zwitterionic monomers, and one or more cationic or anionic monomers are unexpectedly effective for flocculating aqueous suspensions with high conductivity or containing high levels of soluble or colloidal anionic components.
Accordingly, in its principal aspect, this invention is directed to a high molecular weight water-soluble charged polymer comprising from about 50 to about 99.8 mole percent one or more nonionic monomers, from about 0.1 to 9.9 mole percent of one or more cationic or anionic monomers, and from about 0.1 to about 49.9 mole percent of one or more zwitterionic monomers of formula 
wherein
L+ is a group of formula 
Lxe2x88x92 is a group of formula 
W+ is xe2x80x94S+R3xe2x80x94 or xe2x80x94N+R2R3xe2x80x94; 
Z+ is xe2x80x94N+R5R6R7;
R1 and R8 are independently hydrogen or methyl;
R2, R3, R4, R5, R6 and R7 are independently selected from hydrogen and C1-C4 alkyl;
Y1, Y2, and Y3 are independently selected from O or NR2;
m is 2 or 3; and
n is 1-5.
xe2x80x9cAlkylxe2x80x9d means a monovalent group derived from a straight or branched chain saturated hydrocarbon by the removal of a single hydrogen atom. Representative alkyl groups include methyl, ethyl, n- and iso-propyl, n-, sec-, iso- and tert-butyl, and the like. A preferred alkyl group is methyl.
xe2x80x9cReduced specific viscosityxe2x80x9d (RSV) is an indication of polymer chain length and average molecular weight. The RSV is measured at a given polymer concentration and temperature and calculated as follows:   RSV  =            [                        (                      η                          η              o                                )                -        1            ]        c  
wherein xcex7=viscosity of polymer solution;
xcex7o=viscosity of solvent at the same temperature; and
c=concentration of polymer in solution.
As used herein, the units of concentration xe2x80x9ccxe2x80x9d are (grams/100 ml or g/deciliter). Therefore, the units of RSV are dl/g. The RSV is measured at 30xc2x0 C. The viscosities xcex7 and xcex7o are measured using a Cannon-Ubbelohde semimicro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature bath adjusted to 30xc2x10.02xc2x0 C. The error inherent in the calculation of RSV is about 2 dl/g. Similar RSVs measured for two linear polymers of identical or very similar composition is one indication that the polymers have similar molecular weights, provided that the polymer samples are treated identically and that the RSVs are measured under identical conditions.
IV stands for intrinsic viscosity, which is RSV in the limit of infinite polymer dilution (i.e. the polymer concentration is equal to zero). The IV, as used herein, is obtained from the y-intercept of the plot of RSV versus polymer concentration in the range of 0.015-0.045 wt % polymer.
xe2x80x9cCharged polymerxe2x80x9d means a polymer having a net positive or negative charge. The charged polymers of this invention are composed of one or more zwitterionic monomers, one or more nonionic monomers and one or more cationic or anionic monomers. The charged polymers of this invention have a RSV of greater than 5 dl/g when measured at 450 ppm in 1M NaNO3 as described herein. Preferred charged polymers have a RSV of greater than 15 dl/g. More preferred charged polymers have a RSV of greater than 25 dl/g.
xe2x80x9cMonomerxe2x80x9d means a polymerizable allylic, vinylic or acrylic compound. The monomer may be anionic, cationic or nonionic. Vinyl monomers are preferred, acrylic monomers are more preferred.
xe2x80x9cCationic monomerxe2x80x9d means a monomer as defined herein which possesses a net positive charge. Representative cationic monomers include the quaternary or acid salts of dialkylaminoalkyl acrylates and methacrylates, the quaternary or acid salts of dialkylaminoalkylacrylamides and methacrylamides, N,N-diallyldialkyl ammonium halides, Mannich products, and the like. Alkyl groups are generally C1-4 alkyl. Preferred cationic monomers include diallyldimethylammonium chloride (DADMAC), (3-acrylamidopropyl)trimethylammonium chloride (APTAC), (3-methacrylamido)propyltrimethylammonium chloride (MAPTAC), dimethylaminoethylacrylate methyl chloride quaternary salt (DMAEA.MCQ), dimethylaminoethylmethacrylate methyl chloride quaternary salt (DMAEM.MCQ) and dimethylaminoethylacrylate benzyl chloride quaternary salt (DMAEA.BCQ). Dimethylaminoethylacrylate methyl chloride quaternary salt is preferred.
xe2x80x9cAnionic monomerxe2x80x9d means a monomer as defined herein which possesses a net negative charge. Representative anionic monomers include metal salts of acrylic acid, methacrylic acid, or itaconic acid, 2-acrylamido-2-methyl propane sulfonate, sulfopropyl acrylate or methacrylate or other water-soluble forms of these or other polymerizable carboxylic or sulphonic acids, sulphomethylated acrylamide, allyl sulphonate, sodium vinyl sulphonate, and the like. Preferred anionic monomers include acrylic acid, methacrylic acid, 2-acrylamido-2-methyl propane sulfonic acid, monoacryloxyethyl phosphate and their sodium salts.
xe2x80x9cNonionic monomerxe2x80x9d means a monomer as defined herein which is electrically neutral. Representative nonionic monomers include acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-(2-hydroxypropyl)methacrylamide, N-methylolacrylamide, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, poly(ethylene glycol)(meth)acrylate, poly(ethylene glycol) monomethyl ether mono(meth)acrylate, N-vinyl-2-pyrrolidone, glycerol mono((meth)acrylate), 2-hydroxyethyl(meth)acrylate, vinyl methylsulfone, vinyl acetate, and the like. Preferred nonionic monomers include acrylamide and methacrylamide. Acrylamide is more preferred.
xe2x80x9cZwitterionic monomerxe2x80x9d means a polymerizable molecule containing cationic and anionic (charged) functionality in equal proportions, so that the molecule is net neutral overall.
Representative Zwitterionic Monomers Include
N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, 2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine, 2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate, 2-(acryloyloxyethyl)-2xe2x80x2-(trimethylammonium)ethyl phosphate, [(2-acryloylethyl)dimethylammonio]methyl phosphonic acid, 2-methacryloyloxyethyl phosphorylcholine (MPC), 2-[(3-acrylamidopropyl)dimethylammonio]ethyl 2xe2x80x2-isopropyl phosphate (AAPI), 1-vinyl-3-(3-sulfopropyl)imidazolium hydroxide, (2-acryloxyethyl) carboxymethyl methylsulfonium chloride, 1-(3-sulfopropyl)-2-vinylpyridinium betaine, N-(4-sulfobutyl)-N-methyl-N,N-diallylamine ammonium betaine (MDABS), N,N-diallyl-N-methyl-N-(2-sulfoethyl) ammonium betaine, and the like.
Preferred zwitterionic monomers include N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine, N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine and N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine.
N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine is more preferred.
xe2x80x9cZwitterionic polymerxe2x80x9d means a polymer composed from zwitterionic monomers and, possibly, other non-ionic monomer(s) as disclosed in published International Application Number PCT/US00/17841.
The zwitterionic monomers used for preparing the charged polymers of this invention are prepared as shown in Schemes 1 and 2. In Schemes 1 and 2, R1, R2, R3, R4, m and n are as defined herein, and p is 1 or 2. 
As shown in the foregoing Scheme 1, reaction of amine 1 with sultone 2, both available from Aldrich Chemical Co., Milwaukee, Wis., results in formation of the zwitterionic monomer 3. The reaction is conducted in a suitable organic solvent at a temperature of from about 25xc2x0 C. to about 60xc2x0 C. over about 6 to about 36 hours. Representative organic solvents include acetone, tetrahydrofuran, dioxane, ethyl acetate, and the like. The reaction is preferably conducted in acetone at about 30xc2x0 C. to about 50xc2x0 C. over 12-24 hours. 
As shown in the foregoing Scheme 2, reaction of the amine 4 with the alkyl carboxylate 5 results in formation of the zwitterionic monomer 6. In Scheme 2, X represents any leaving group which may be displaced by the nucleophilic nitrogen atom of amines 4 and 7 under the conditions described herein. Representative leaving groups include halogen, tosylate, mesylate, and the like. A preferred leaving group is chloro. The reaction is conducted in water or in a mixture of water and a water-soluble organic solvent such that the acetate salt is soluble at a temperature of from about 25xc2x0 C. to about 60xc2x0 C. over about 6 to about 36 hours. Representative organic solvents include acetone, tetrahydrofuran, dioxane, and the like. The reaction is preferably conducted in water at about 30xc2x0 C. to about 50xc2x0 C. over 12-24 hours. Alternatively, as also shown in Scheme 2, the amine 7 may be allowed to react with an ester of the chloro- or bromomethylacetate, for example, in a suitable organic solvent to form a cationic intermediate, which can be isolated, purified, and subsequently hydrolyzed to the zwitterionic monomer under aqueous conditions.
The high molecular weight water-soluble charged polymers of this invention are composed of one or more zwitterionic monomers, one or more nonionic monomers, and one or more anionic or cationic monomers.
In a preferred aspect of this invention, the cationic monomers are selected from the group consisting of dimethylaminoethylacrylate methyl chloride quaternary salt, diallyldimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, (3-methacrylamido)propyltrimethylammonium chloride, dimethylaminoethylmethacrylate methyl chloride quaternary salt and dimethylaminoethylacrylate benzylchloride quaternary salt.
In another preferred aspect, the anionic monomers are selected from the group consisting of acrylamidopropanesulfonic acid, acrylic acid, methacrylic acid, monoacryloxyethyl phosphate and their sodium salts.
In another preferred aspect, the high molecular weight water-soluble polymer comprises about 95 to about 99.8 mole percent of a nonionic monomer, about 4.9 to about 0.1 mole percent of a zwitterionic monomer and from about 4.9 to about 0.1 mole percent of a cationic monomer.
In another preferred aspect, the high molecular weight water-soluble polymer comprises about 95 to about 99.8 mole percent of a nonionic monomer, about 4.9 to about 0.1 mole percent of a zwitterionic monomer and from about 4.9 to about 0.1 mole percent of a anionic monomer.
In another preferred aspect, the nonionic monomers are selected from acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-(2-hydroxypropyl)methacrylamide, N-methylolacrylamide, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, poly(ethylene glycol)(meth)acrylate, poly(ethylene glycol) monomethyl ether mono(meth)acrylate, N-vinyl-2-pyrrolidone, glycerol mono((meth)acrylate), 2-hydroxyethyl(meth)acrylate, vinyl methylsulfone and vinyl acetate.
In another preferred aspect, the nonionic monomers are selected from acrylamide and methacrylamide.
In another preferred aspect, the nonionic monomer is acrylamide.
In another preferred aspect, the nonionic monomer is acrylamide and the zwitterionic monomer is 
In another preferred aspect, the nonionic monomer is acrylamide and the zwitterionic monomer is 
In another preferred aspect, the nonionic monomer is acrylamide and the zwitterionic monomer is 
In another preferred aspect, the nonionic monomer is acrylamide and the zwitterionic monomer is selected from
N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine,
N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine,
N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine,
N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine,
2-(methylthio)ethyl methacryloyl-S-(sulfopropyl)-sulfonium betaine,
2-[(2-acryloylethyl)dimethylammonio]ethyl 2-methyl phosphate,
2-(acryloyloxyethyl)-2xe2x80x2-(trimethylammonium)ethyl phosphate and
[(2-acryloylethyl)dimethylammonio]methyl phosphonic acid.
In another preferred aspect, the nonionic monomer is acrylamide and the zwitterionic monomer is selected from
N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine,
N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine,
N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine and
N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine.
In another preferred aspect, the nonionic monomer is acrylamide, the zwitterionic monomer is N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine and the cationic monomer is dimethylaminoethylacrylate methyl chloride quaternary salt.
In another preferred aspect, the nonionic monomer is acrylamide, the zwitterionic monomer is N,N-dimethyl-N-methacrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine and the anionic monomer is acrylamidopropanesulfonic acid sodium salt.
As discussed herein, the preparation of high molecular weight polymers and copolymers of acrylamide as homogeneous solutions in water is difficult because of the extremely high viscosities encountered. High solution viscosities are detrimental for a number of reasons, one being the loss of the ability to mix the reaction mixture and another being the loss of the ability to effectively remove heat from the reactor. Fortunately, two general methods exist which do allow for the production of high molecular weight acrylamide containing polymers and copolymers. The first method, which consists of polymerizing monomer(s) within a dispersed phase, is typified by inverse emulsion polymerization or dispersion polymerization. In the case of an inverse emulsion polymerization, the dispersed phase is formed prior to the polymerization, while in the case of a dispersion polymerization, the xe2x80x9cdispersedxe2x80x9d phase containing the polymer forms during the polymerization. The second method for preparing high molecular weight polymers and copolymers of acrylamide consists of conducting a gel polymerization to produce the polymer product as a dry powder.
xe2x80x9cInverse emulsion polymerxe2x80x9d and xe2x80x9clatex polymerxe2x80x9d mean an invertible water-in-oil polymer emulsion comprising a zwitterionic polymer according to this invention in the aqueous phase, a hydrocarbon oil for the oil phase, a water-in-oil emulsifying agent and, potentially, an inverting surfactant. Inverse emulsion polymers are hydrocarbon continuous with the water-soluble polymers dispersed as micron sized particles within the hydrocarbon matrix. The advantages of polymerizing water-soluble monomers as inverse emulsions include 1) low fluid viscosity can be maintained throughout the polymerization, permitting effective mixing and heat removal, 2) the products can be pumped, stored, and used easily since the products remain liquids, and 3) the polymer xe2x80x9cactivesxe2x80x9d or xe2x80x9csolidsxe2x80x9d level can be increased dramatically over simple solution polymers, which, for the high molecular weight flocculants, are limited to lower actives because of viscosity considerations. The inverse emulsion polymers are then xe2x80x9cinvertedxe2x80x9d or activated for use by releasing the polymer from the particles using shear, dilution, and, generally, another surfactant, which may or may not be a component of the inverse emulsion.
Inverse emulsion polymers are prepared by dissolving the desired monomers in the aqueous phase, dissolving the emulsifying agent(s) in the oil phase, emulsifying the water phase in the oil phase to prepare a water-in-oil emulsion, in some cases, homogenizing the water-in-oil emulsion, polymerizing the monomers dissolved in the water phase of the water-in-oil emulsion to obtain the polymer as a water-in-oil emulsion. If so desired, a self-inverting surfactant can be added after the polymerization is complete in order to obtain the water-in-oil self-inverting emulsion.
The oil phase comprises any inert hydrophobic liquid. Preferred hydrophobic liquids include aliphatic and aromatic hydrocarbon liquids including benzene, xylene, toluene, paraffin oil, mineral spirits, kerosene, naphtha, and the like. A paraffinic oil is preferred.
Free radical yielding initiators such as benzoyl peroxide, lauroyl peroxide, 2,2xe2x80x2-azobis (isobutyronitrile) (AIBN), 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) (AIVN), potassium persulfate and the like are useful in polymerizing vinyl and acrylic monomers. 2,2xe2x80x2-azobis(isobutyronitrile) (AIBN) and 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) (AIVN) are preferred. The initiator is utilized in amounts ranging between about 0.002 and about 0.2 percent by weight of the monomers, depending upon the solubility of the initiator.
Water-in-oil emulsifying agents useful for preparing the latex polymers of this invention include sorbitan esters of fatty acids, ethoxylated sorbitan esters of fatty acids, and the like or mixtures thereof. Preferred emulsifying agents include sorbitan monooleate, polyoxyethylene sorbitan monostearate, and the like. Additional details on these agents may be found in McCutcheon""s Detergents and Emulsifiers, North American Edition, 1980. Any inverting surfactant or inverting surfactant mixture described in the prior art may be used. Representative inverting surfactants include ethoxylated nonylphenol, ethoxylated linear alcohols, and the like. Preferred inverting surfactants are ethoxylated linear alcohols.
The polymer is prepared by polymerizing the appropriate monomers at from about 30xc2x0 C. to about 85xc2x0 C. over about 1 to about 24 hours, preferably at a temperature of from about 40xc2x0 C. to about 70xc2x0 C. over about 3 to about 6 hours.
xe2x80x9cDispersionxe2x80x9d polymers mean a water-soluble polymer dispersed in an aqueous continuous phase containing one or more inorganic salts. Representative examples of dispersion polymerization of water-soluble polymers in an aqueous continuous phase can be found in U.S. Pat. Nos. 4,929,655, 5,006,590, 5,597,859 and 5,597,858 and in European Patent Nos. 657,478 and 630,909.
Dispersion polymers are prepared by combining water, one or more inorganic salts, one or more water-soluble monomers, any polymerization additives such as chelants, pH buffers or chain transfer agents, and a water-soluble stabilizer polymer. This mixture is charged to a reactor equipped with a mixer, a thermocouple, a nitrogen purging tube, and a water condenser. The monomer solution is mixed vigorously, heated to the desired temperature, and then a water-soluble initiator is added. The solution is purged with nitrogen whilst maintaining temperature and mixing for several hours. During the course of the reaction, a discontinuous phase containing the water-soluble polymer is formed. After this time, the products are cooled to room temperature, and any post-polymerization additives are charged to the reactor. Water continuous dispersions of water-soluble polymers are free flowing liquids with product viscosities generally 100-10,000 cP, as measured at low shear. The advantages of preparing water-soluble polymers as water continuous dispersions are similar to those already mentioned in association with the inverse emulsion polymers. The water continuous dispersion polymers have the further advantages that they contain no hydrocarbon oil or surfactants, and require no surfactant for xe2x80x9cinversionxe2x80x9d or activation.
A xe2x80x9cgelxe2x80x9d polymerization is defined as a process for producing polymers as dry powders. The preparation of high molecular weight water-soluble polymers as dry powders using a gel polymerization is generally performed as follows: an aqueous solution of water-soluble monomers, generally 20-60 percent concentration by weight, along with any polymerization or process additives such as chain transfer agents, chelants, pH buffers, or surfactants, is placed in an insulated reaction vessel equipped with a nitrogen purging tube. A polymerization initiator is added, the solution is purged with nitrogen, and the temperature of the reaction is allowed to rise uncontrolled. When the polymerized mass is cooled, the resultant gel is removed from the reactor, shredded, dried, and ground to the desired particle size.
The water-soluble charged polymers of this invention are useful as retention and drainage aids in the manufacture of paper and as a flocculant for removing suspended solids from white water in the papermaking process with particular importance for mechanical grades with high amounts of xe2x80x9canionic trashxe2x80x9d.
Mechanical pulping often produces paper furnishes which can be problematic to flocculate. In mechanical pulps, approximately 1-5% of the wood is transformed into soluble components contained in the process water. Due to inefficient washing of mechanical pulps (particularly bleached pulps), the dissolved and colloidal substances (DCS) are transferred to the paper machine where they can interfere with papermaking. The DCS is often anionically charged and is often referred to as anionic trash. The presence of DCS can dramatically effect the flocculation and drainage performance of additives described above which are designed to improve such processes. In highly closed systems, DCS may accumulate to high concentrations that are detrimental to optimum machine operation and/or product quality. Furthermore, fluctuations in bleaching levels can cause variations in DCS concentrations. DCS variability creates poor process control over the retention and drainage performance when additive effectiveness is DCS dependent. Thus, pulps with high and/or varying DCS levels or containing specific charged species detrimental to traditional flocculants require more specialized flocculants to maintain effective/efficient retention and drainage performance.
Accordingly, in another aspect, this invention is directed to a method of removing suspended solids and clarifying white water in the papermaking process comprising adding to the white water, pulp washers, or thickeners an effective flocculating amount of the high molecular weight water-soluble charged polymer of this invention.
In another aspect, this invention is directed to a method of increasing filler retention in a papermaking furnish comprising adding an effective flocculating amount of the high molecular weight water-soluble charged polymer of this invention to the filler slurry prior to addition to the papermaking furnish.
In another aspect, this invention is directed to a method for increasing retention and drainage in fibrous suspensions of pulp during processing of said pulp comprising adding to the pulp an effective amount of the high molecular weight water-soluble charged polymer of this invention.
The effective amount of the charged polymer depends on the characteristics of the particular papermaking furnish and can be readily determined by one of ordinary skill in the papermaking art. Typical dosages are from about 0.01 to about 6, preferably from about 0.1 to about 4 and more preferably from about 0.1 to about 2 pounds polymer actives/ton solids in the furnish.
The charged polymer of this invention may also be used in combination with a coagulant as part of a dual polymer treatment program. Preferred coagulants are water-soluble cationic polymers such as epichlorohydrin-dimethylamine or polydiallyldimethylammonium chloride, alum, polyaluminum chlorides or cationic starch.
In a preferred aspect, adding bentonite, synthetic clays, microparticles, or resin enhancers are added to the pulp.
xe2x80x9cMicroparticlexe2x80x9d means highly charged materials that improve flocculation when used together with natural and synthetic macromolecules. The use of microparticles to improve the retention and drainage properties of a furnish is described in U.S. Pat. Nos. 4,753,710 and 4,913,775 incorporated herein by reference. Microparticles encompass a broad set of chemistries including polysilicate microgel, structured colloidal silicas, colloidal alumina, polymers including copolymers of acrylic acid and acrylamide and naphthalene sulfonate/formaldehyde condensate polymers, bentonite and mineral clays such as montmorillonite, saponite and smectite types and colloidal silica in its many forms including modified colloidal silicic acids such as those described in PCT/US98/19339.
Representative copolymers of acrylic acid and acrylamide useful as microparticles include Nalco(copyright) 8677 PLUS, available from ONDEO Nalco Company, Naperville, Ill., USA. Other copolymers of acrylic acid and acrylamide are described in U.S. Pat. No. 5,098,520, incorporated herein by reference.
xe2x80x9cBentonitesxe2x80x9d include any of the materials commercially referred to as bentonites or as bentonite-type clays, i.e., anionic swelling clays such as sepialite, attapulgite and montmorillonite. In addition, the bentonites described in U.S. Pat. No. 4,305,781 are suitable. A preferred bentonite is a hydrated suspension of powdered bentonite in water. Powdered bentonite is available as Nalbrite(trademark), from ONDEO Nalco Company.
Representative dispersed silicas have an average particle size of from about 1 to about 100 nanometers (nm), preferably from about 2 to about 25 nm, and more preferably from about 2 to about 15 nm. This dispersed silica, may be in the form of colloidal, silicic acid, silica sols, fumed silica, agglomerated silicic acid, silica gels, precipitated silicas, and all materials described in Patent Cooperation Treaty Patent Application No. PCT/US98/19339, so long as the particle size or ultimate particle size is within the above ranges. Dispersed colloidal silica in water with a typical particle size of 4 nm is available as Nalco(copyright) 8671, from ONDEO Nalco Company. Another type of inorganic colloid used as a microparticle is a borosilicate in water; available as Nalco(copyright) 8692, from ONDEO Nalco Company. Other types of colloidal silica and modified colloidal silicas are commercially available from E.I. DuPont de Nemours and Co., Wilmington, Del. under the tradename Ludox(copyright), from Akzo Nobel, Surte, Sweden (BMA or NP Series), from Vinings Industries Inc., Atlanta, Ga. and from Nissan Chemical Industries, Ltd., Tokyo, Japan.
Representative naphthalene sulfonate/formaldehyde condensate polymers include Nalco(copyright) 8678 from Nalco Chemical Company.
The amount of microparticle added is from about 0.05 to about 10, preferably from about 0.1 to about 9 and more preferably about 0.2 to about 6 pounds microparticle/ton.
xe2x80x9cPounds microparticle/tonxe2x80x9d means pounds of actual microparticle per 2000 pounds of solids present in slurry. The abbreviation for pounds of actual microparticle per 2000 pounds of solids present in slurry is xe2x80x9clbs microparticle/tonxe2x80x9d.
The microparticle is added to the papermaking furnish either before or after the structurally modified polymer is added to the furnish. The choice of whether to add the microparticle before or after the polymer can be made by a person of ordinary skill in the art based on the requirements and specifications of the papermaking furnish.
In a preferred aspect of this invention, the microparticle is bentonite.